Casimir patron saint of Poland, was grand-duke of Lithuania, and third son of Casimir IV, born Oct. 5, ,1458, and was educated by John Dugoff, a canon of Cracow, commonly called Longinus. Casimir, in early youth, devoted himself to piety and self-denial. When the nobles of Hungary, dissatisfied with Matthias Corvinus, their king, entreated the king of Poland to send his son Casimir to occupy the throne, the latter, with extreme reluctance, went thither; but finding that the differences between Matthias and his people were adjusted, he joyfully returned home, and spent the rest of his life in exercises of devotion. He died of consumption, at Wilna, in Lithuania, March 4, 1482. He was canonized by pope Leo X. The day of his commemoration is March 4. See Landon, Eccles. Dict. s.v.; Hoefer, Nouv. Biog. Géneralé, s.v.